Sterling reaches a contact at the CDC and a medical team arrives to safely transport Leila to hospital. Using Sophia's laptop, Sterling uncovers the three locations where the virus will be released - a food processing plant, the US bureau of engraving and Dallas airport. Sterling contacts Martinez and informs him of Sophia's plans, but he explains that he cannot take action until he is reinstated as President. Chief of Staff Peel dispatches two covert teams to the food plant and the engraving bureau, but Sterling and his team - including Simon, Sean and Vicky - realise that they will have to stop Sophia's plot at the airport themselves. Meanwhile, the portal array is activated and the Earth begins to suffer from atmospheric disturbances and violent earthquakes.

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Martinez confronts Acting-President Jarvis and threatens to expose him as a traitor if he does not authorise the shutdown of Dallas airport, but the cocky Jarvis refuses, convinced that Martinez has no concrete evidence of his misdeeds. Elsewhere, Sophia and Carlos secretly meet with a sleeper agent named Delgado, who works at the airport. Delgado takes two virus canisters from them and hands over a card that will allow the pair to bypass security. Meanwhile, at the food processing plant, one covert team moves in and takes out the sleeper agents before they are able to release their portion of the virus. A second team secures the canister at the bureau of engraving, but a sleeper named Devon is able to call Sophia and warn her that their plan has failed before he is killed.

Sterling, Simon, Sean and Vicky arrive at the airport and split up, with the former two searching for Delgado while the latter pair hunt down Sophia. Sterling and Simon hold an airport guard at gunpoint and force their way into an off-limits area. They spot Delgado and give chase, but the sleeper shoots Simon in the chest. Though he is wearing a vest and is not badly hurt, Delgado is able to escape. When Sterling calls Sean and informs him of Delgado's location, he and Vicky break into another secure area, knocking a guard unconscious. Meanwhile, the cabinet assembles at the White House to discuss Martinez's reinstatement. The former President is welcomed back by his staff, but suffers a relapse and collapses.

Delgado meets with Sophia and Carlos and returns the canisters to them. Sean and Vicky catch up to them, but are met by a hail of bullets. Vicky returns fire, killing Delgado. While Carlos and Vicky exchange fire, Sean chases after Sophia. With Vicky pinned down, Carlos prepares to open his canister, but Sterling arrives in the nick of time and shoots him dead. Back at the White House, the cabinet prepares to disband, leaving Jarvis as President, but Martinez returns and accuses Jarvis of being behind his recent brush with death. Though the Acting-President denies the charges, Martinez plays back a recording of their early conversation, in which Jarvis admitted his part in the poisoning. With Jarvis's betrayal revealed, Martinez is quickly reinstated, and orders that Dallas airport be shut down.

At the airport, Sean pursues Sophia, but the alien leader locks herself in a departure lounge. As Military teams arrive at the airport, all exits from the building are sealed. Sean tries to reason with Sophia, insisting that her plan to cull the human race has failed and that the release of the virus is now tantamount to murder. Moved by Sean's pleas to put an end to everybody's pain, Sophia does not release the virus and surrenders to the military.

In the aftermath, Simon warns Sean that the crisis is not over and that his people are still coming to Earth. Simon explains that his people originally resided on Earth, but left to avoid a cataclysmic occurrence - The Event - that would see them evolve into something greater, but completely decimate the human race. Simon is summoned to the White House, but tells Sean that the answers he seeks are held in Dempsey's scroll. Meanwhile, Sterling and President Martinez share a happy reunion, and Martinez also thanks Simon for saving his life. Simon confirms that 2 and a half billion of his people are still coming to Earth, and Chief of Staff Peel reveals that Jarvis previously instructed the NSA to redirect a surveillance satellite positioned over an area in Tibet.

As the satellite is redirected to its original position, Martinez, Sterling, Simon and Peel spot the active portal array. Meanwhile, Sean is cleared to visit Leila. Before he goes in, Vicky thanks Sean for keeping her family safe and helping her to fight for good. The pair share an emotional embrace, then part ways. Sean visits Leila in isolation and insists that the doctors will find a way to cure her. Leila also shares happy news with an overjoyed Sean - the doctors have discovered that she is pregnant.

Back at the White House, Sophia is brought before Martinez, Sterling and Simon. She insists that the release of the virus was an act of mercy and warns them that when her people arrive, something much worse will occur. Suddenly, the entire planet begins to tremble as an enormous portal opens in deep space. An entire planet comes through from the other side and lingers menacingly in the sky. When her young son asks what the planet is, First Lady Christina Martinez softly replies, "Home."

What did you make of The Event's series finale? Sad there'll be no second season? Sound off below!